The present invention relates to a retroreflection mirror device, and in particular to a polarization-dependent retroreflection mirror device using a pair of birefringent wedges to direct beams of light, preferably for use in an optical channel interleaver device.
Retroreflection mirrors are used in optics to reflect an optical beam back along a path parallel to the incident beam, with a desired offset therefrom. Conventional devices use Right Angle Prisms, either alone or in various combinations thereof for retroreflection. Right Angle Prisms reflect light independent of the polarization thereof. Moreover, the reflection direction is independent to the angle at which the beam is incident upon the mirror. Unfortunately, the offset of the reflected beam is very sensitive to the position of the incident beam relative to the prism. FIG. 1 illustrates how, if the prism is offset by a distance y from a desired position thereof, the reflected beam will be displaced by a distance 2y from its desired location. Similarly, with reference to FIG. 2, if the incident beam is offset by a distance y from the ideal position thereof, the reflected beam will also be displaced by a distance y from its desired location.
Other potential errors in Right Angle Prisms result from structural errors inherent in the prisms themselves. Inaccuracies in the right angle and the pyramidal angle result in errors that are three times larger than the original error (see FIGS. 3a and 3b). In the fiber optic communication industry, in which very small components requiring precise optical alignment are packed into minimally sized packages, it is advantageous to have devices that are much less sensitive to minor misalignments.
It is an object of the present invention to overcome the shortcomings of the prior art by providing a retroreflection mirror that is relatively much less sensitive to incident beam angle and position.
Accordingly the present invention relates to a retroreflection mirror device comprising:
beam-directing means including a first wedge having a first optical axis, and a second wedge having a second optical axis that is perpendicular to the first optical axis, the beam directing means for receiving a first optical signal having a first polarization along a first incident axis, and for directing the first optical signal outwardly therefrom at a first angle from a first launch axis, the first launch axis being parallel to the incident axis;
polarization rotating means for effectively rotating the polarization of the first optical signal by 90xc2x0; and
a reflector for directing the first optical signal back through the beam-directing means;
whereby after passing through the beam-directing means a second time the first optical signal exits the beam-directing means along a first output axis substantially parallel to the first incident axis.
Another aspect of the present invention relates to a deinterleaver apparatus comprising:
a first port for inputting a first polarized optical signal, which comprises a second optical signal with a first subset of channels and a third optical signal with a second subset of channels;
a second port for outputting the second optical signal;
a third port for outputting the third optical signal;
a birefringent assembly optically coupled to the first, second and third ports, whereby, after the first optical signal makes a first pass through the birefringent assembly along a first path, the second optical signal exits the birefringent assembly with a polarization orthogonal to the polarization of the third optical signal;
beam-directing means including a first wedge having a first optical axis, and a second wedge having a second optical axis that is perpendicular to the first optical axis, the beam directing means for receiving the first optical signal along the first path, and for directing the second and third optical signals outwardly therefrom with a launch angle therebetween;
polarization rotating means for effectively rotating the polarization of the second and third optical signals by 90xc2x0; and
a reflector for directing the second and third optical signals back through the beam-directing means;
whereby, after passing through the beam-directing means a second time, the second and third optical signals: exit the beam-directing means along second and third paths, respectively, which are substantially parallel to the first path; pass through the birefringent assembly for a second time; and exit via the second and third ports, respectively.
Another feature of the present invention relates to an interleaver apparatus comprising:
a first port for outputting a first polarized optical signal, which comprises a second optical signal with a first subset of channels and a third optical signal with a second subset of channels;
a second port for inputting the second optical signal;
a third port for inputting the third optical signal;
a birefringent assembly optically coupled to the first, second and third ports, whereby, after the second and third optical signals make a first pass through the birefringent assembly along second and third paths, the second optical signal exits the birefringent assembly with a polarization orthogonal to the polarization of the third optical signal;
beam-directing means including a first wedge having a first optical axis, and a second wedge having a second optical axis that is perpendicular to the first optical axis, the beam directing means for receiving the second and third optical signals along the second and third paths, respectively, for directing the second optical signal outwardly therefrom at a first angle from a first launch axis, and for directing the third optical signal outwardly therefrom at a second angle from a second launch axis, the first and second launch axes being parallel to the second and third paths;
polarization rotating means for effectively rotating the polarization of the second and third optical signals by 90xc2x0; and
a reflector for directing the second and third optical signals back through the beam-directing means;
whereby, after passing through the beam-directing means a second time, the second and third optical signals: exit the beam-directing means together along a first path, which is substantially parallel to the second and third paths; pass through the birefringent assembly for a second time; and exit via the first port.